CDKN2A novel mutation in a patient from a melanoma-prone family

Genetics of melanoma predisposition

Predisposition to melanoma is genetically heterogeneous. Two high penetrance susceptibility genes, CDKN2A and CDK4, have so far been identified and mapping is ongoing to localize and identify others. With the advent of a catalogue of millions of potential DNA polymorphisms, attention is now also being focused on identification of genes that confer a more modest contribution to melanoma risk, such as those encoding proteins involved in pigmentation, DNA repair, cell growth and differentiation or detoxification of metabolites. One such pigmentation gene, MC1R, has not only been found to be a low penetrance melanoma gene but has also been shown to act as a genetic modifier of melanoma risk in individuals carrying CDKN2A mutations. Most recently, an environmental agent, ultraviolet radiation, has also been established as a modifier of melanoma risk in CDKN2A mutation carriers. Hence, melanoma is turning out to be an excellent paradigm for studying gene-gene and gene-environment interactions.

Mutational analysis of CDKN2A genes in patients with squamous cell carcinoma of the skin

BACKGROUND

Nonmelanoma skin cancers [squamous cell carcinomas (SCC) and basal cell carcinomas (BCC)] are the most common neoplasias of the Caucasian population.

OBJECTIVES

The purpose of our study was to determine the involvement of CDKN2A genes in the development of sporadic nonmelanoma skin cancer in Greek patients.

PATIENTS AND METHODS

Allelic imbalance analysis was performed in 22 SCC and five Bowen's disease specimens. Mutational analysis was performed on exons 1alpha, 1beta and 2 of the CDKN2A locus in 22 SCC, five Bowen's disease and 39 BCC specimens. Exon 1alpha was additionally screened in 28 BCC specimens to complete the mutational analysis of a previous study.

RESULTS

Overall, 52% (14 of 27) of the SCC and Bowen's disease specimens exhibited loss of heterozygosity (LOH) in at least one microsatellite marker, whereas, only two of 27 (7%) exhibited microsatellite instability. LOH in 9p appears to be equally involved in both BCC and SCC tumours. Exons 1alpha, 1beta and 2 of the CDKN2A locus were screened for mutations. A Val28Gly substitution in exon 1alpha and a CCC-->TTT (Ala57Val and Arg58Ter) substitution in exon 2, resulting in a change in the amino acid sequence, are reported for the first time in two SCCs, the latter being indicative of a combination of an ultraviolet (UV) radiation-induced mutation and a point mutation. A previously described polymorphism of CDKN2A, the gene for p16INK4a, Ala148Thr, was also detected in an allelic frequency of 3.72%. No mutation was found in any of the five Bowen's disease specimens, or in exon 1beta of CDKN2A, also the gene for p14ARF.

CONCLUSIONS

Mutations and the high incidence of 9p LOH detected in our SCC samples imply that inactivation of CDKN2A genes, via allelic loss and/or mutation (probably UV-induced) may play a significant role in nonmelanoma skin cancer development, particularly in the more aggressive SCC type.